Bags made of thin polyethylene material have been used in various sizes. Small bags are used in packaging of sandwiches and the like. Larger bags are used as shopping bags. Even larger bags are used for containing trash.
A particularly advantageous closure for such a bag includes a draw tape made from the same polyethylene material as the bag. U.S. Pat. No. 3,029,853--Piazzi, British Pat. No. 1,125,363 Jortikka, U.S. Pat. No. 4,558,463--Boyd and U.S. Pat. No. 4,624,654--Boyd et al are examples of draw tape bags. Such closures have been successfully employed in these bags.
Draw tape closures for large trach bags, and the manufacture of these draw tape trash bags, are described in the aforesaid U.S. Pat. Nos. 4,558,463 and 4,624,654. Other related patents are U.S. Pat. No. 4,617,008--Boyd et al which describes a hem forming apparatus and U.S. Pat. No. 4,597,750--Boyd et al which describes the apparatus for inserting a draw tape into the bag. Bags having intermittently oriented draw tapes are disclosed in related U.S. Pat. No. 4,628,536--Herrington. The disclosures of the foregoing related patents are incorporated herein by reference.
In the past, thermoplastic bag structures with integral handle elements formed as an integral part of the bag structure itself have been produced by a method which reduces stress concentration. Stress points around the bag mouth are distributed to areas which are less likely to rupture as a result of stress concentration. See U.S. Pat. No. 4,165,832--Kuklies et al. This patent discloses a thermoplastic bag structure with integral handle elements, ie.e. the handles are actually an extension of the bag proper and stres relief notches positioned at opposite ends of the mouth.
Previous handle configurations for thermoplastic bags have been characterized by exhibiting the effect of "roping" while the bag is under load. According to the Kuklies et al patent, stress concentration causes a thermoplastic handle to form a rope while under load, such rope having a diameter given by the following formula: EQU D=(8 WG/.pi.) 1/2
where D is the equivalent diameter of the "rope" (in.), W is the width of the handle structure (in.), and G is the gauge (mils) of the handle structure.
A decrease in the gauge of the thermoplastic handle exhibiting the above characteristic would give a rope of a decreased diameter. A thermoplastic bag handle forming a rope of a smaller diameter will cause more discomfort to the carrier of such a bag, due to a decreased area of distribution of the weight of the bag upon the hand of the carrier.
Draw tape bags have a draw tape that is a separate structure from the bag proper. Draw tape trash bags of the type made according to the above-mentioned Boyd et al patents normally have a 1" wide draw tape for the full width of the bag. When the tape is pulled hard to close the bag, it elongates over most of its length, and the area where it is gripped by the hand becomes narrow, or "ropes" and hurts the hand. It is possible to make a draw tape that is sufficiently strong at thin gauges, such as 1.5 mils, but this tape is unsatisfactory for use because of the "roping" effect. As a result, it has been customary to use a tape material that is thicker, thus more costly then that which is required for performance. For example, tape thicknesses that have been used are in the order of 3 to 4 mils, about twice what is actually required.
It is desirable to produce a thermoplastic bag handle of a smaller gauge, less costly material, while substantially preventing "roping" at the area of the handle held by the hand of the carrier.